General, Organic, and Biological Chemistry Chemical Reactions II – Oxidation Reduction, Chemical Kinetics and Chemical Equilibrium General, Organic, and Biological Chemistry

Oxidation-Reduction Reactions An oxidation–reduction reaction Can fall in any one of the 4 basic type of reaction categories Involves transfer of electrons from one reactant to the other provides us with energy from food provides electrical energy in batteries occurs when iron rusts 4Fe(s) + 3O2(g) 2Fe2O3(s) General, Organic, and Biological Chemistry

Transfer of Electrons in Oxidation-Reduction Reactions Zn(s) + CuSO4(aq)  ZnSO4 (aq) + Cu(s) An oxidation–reduction reaction transfers electrons from one reactant to another Oxidation Is a Loss of electrons (OIL) Zn(s) Zn2+(aq) + 2e Reduction Is a Gain of electrons (RIG) Cu2+(aq) + 2e Cu(s)

Oxidation and Reduction - electron transfer Reactant A transfers an Electron to Reactant B. Reactant A becomes oxidized. Reactant B becomes reduced

Oxidized or Reduced?

Oxidation–Reduction in Biological Systems In biological systems, oxidation may involve the loss of H the gain of O In biological systems, reduction may involve the gain of H the loss of O

Summary of Oxidation and Reduction

Chapter 6 Chemical Reactions and Quantities General, Organic, and Biological Chemistry

Reaction Conditions Reaction conditions for a chemical reaction require collisions between reacting molecules collisions with sufficient energy to break the bonds in the reactants the breaking of bonds between atoms of the reactants the forming of new bonds to give products General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Collision Theory of Reactions A chemical reaction occurs when collisions between molecules have sufficient energy to break the bonds in the reactants molecules collide with the proper orientation bonds between atoms of the reactants (N2 and O2) are broken and new bonds (NO) form General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Chemical Reactions In the reaction H2(g) + I2(g) 2HI(g), the reactants H2 and I2 collide the bonds of H2 and I2 break the bonds for HI form H2 + I2 collision bonds break HI new bonds form General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Activation Energy Activation energy is the minimum energy required upon collision for a reaction to take place General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Heat of Reaction The heat of reaction is the amount of heat absorbed or released during a reaction is the difference in the energy of the reactants and the products Heat content of a system is related to the enthalpy = H Heat of reaction is the change in enthalpy = ΔH ΔH = ΔHproducts − ΔHreactants General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Exothermic Reactions In an exothermic reaction, the energy of the products is less than the energy of the reactants heat of reaction is released heat is a product C(s) + O2(g) CO2(g) + 394 kJ ΔH = –394 kJ/mole (heat released) General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Endothermic Reactions In an endothermic reaction, heat is absorbed the energy of the products is greater than the energy of the reactants heat is a reactant N2(g) + O2(g) + 180 kJ 2NO(g) ΔH = 180 kJ (heat added) General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Summary Reaction Energy Heat Sign of Type Change in Reaction ΔH Endothermic Heat absorbed Reactant side + Exothermic Heat released Product side – General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Activation Energy – Affects reaction rates (kinetics) Reaction rate can be increased by increasing concentration of reactants decreasing activation energy The activation energy is the minimum energy needed for a reaction to take place upon proper collision of reactants Lower activation energy, speed up reaction Activation energy lowered by increasing T a catalyst General, Organic, and Biological Chemistry

Reversible Reactions In a reversible reaction, there are both forward and reverse reactions. Suppose SO2 and O2 are present initially. As they collide, the forward reaction begins. 2SO2(g) + O2(g) 2SO3(g) As SO3 molecules form, they also collide in the reverse reaction that forms reactants. This reversible reaction is written with a double arrow. forward reverse General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

General, Organic, and Biological Chemistry Chemical Equilibrium the rate of the forward reaction = equal to the rate of the reverse reaction there is no further change in the amounts of reactant and product General, Organic, and Biological Chemistry

Equilibrium At equilibrium, the forward reaction of N2 and O2 forms NO the reverse reaction of 2NO forms N2 and O2 the amounts of N2, O2, and NO remain constant N2(g) + O2(g) 2NO(g) General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Chemical Equilibrium General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Equilibrium Constants For the reaction aA bB The equilibrium constant expression, Kc, gives the concentrations of the reactants and products at equilibrium: Kc = [B]b = [Products] [A]a [Reactants] The square brackets indicate the moles/liter of each substance. The coefficients b and a are written as superscripts that raise the moles/liter to a specific power. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Writing a Kc Expression Write the Kc expression for the following: STEP 1 Write the balanced equilibrium equation: 2CO(g) + O2(g) 2CO2(g) STEP 2 Write the product concentrations in the numerator and the reactant concentration in the denominator: Kc = [CO2] [products] [CO][O2] [reactants] STEP 3 Write the coefficients as superscripts: Kc = [CO2]2 [CO]2 [O2] General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Learning Check The Kc expression for the following reaction is: 2KClO3(s) 2KCl(s) + 3O2(g) 1) [KCl][O2] 2) [KCl]2[O2]3 [KClO3] [KClO3]2 3) [KCl]2[O2]3 4) [O2]3 General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Le Châtelier’s Principle Le Châtelier’s principle states that any change in equilibrium conditions upsets the equilibrium of the system a system at equilibrium under stress will shift to relieve the stress there will be a change in the rate of the forward or reverse reaction to return the system to equilibrium NOTE: Catalysts only increase reaction rate, NOT equilibrium General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Effect of Adding Reactant or Product Consider the following reaction at equilibrium. H2(g) + F2(g) 2HF(g) If more reactant (H2 or F2) is added, there is an increase in the number of collisions. The rate of the forward reaction increases and forms more HF product until new equilibrium concentrations equal Kc again. The effect of adding a reactant shifts the equilibrium toward the products (shift to right). The opposite happens if more product was added (shift to the left). General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Adding Reactant or Product The equilibrium shifts toward products when H2(g) or F2(g) is added reactants when HF(g) is added H2(g) + F2(g) 2HF(g) Add H2 or F2 Add HF General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Exothermic Reactions In an exothermic reaction, the energy of the products is less than the energy of the reactants heat of reaction is released heat is a product C(s) + O2(g) CO2(g) + 394 kJ ΔH = –394 kJ/mole (heat released) General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Endothermic Reactions In an endothermic reaction, heat is absorbed the energy of the products is greater than the energy of the reactants heat is a reactant N2(g) + O2(g) + 180 kJ 2NO(g) ΔH = 180 kJ (heat added) General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Heat, Endothermic and Exothermic Reactions For an endothermic reaction at equilibrium, decrease in temp (T) shifts toward the reactants increase in temp shifts toward products. CaCO3(s) + 133 kcal CaO(s) + CO2(g) For an exothermic reaction at equilibrium, increase in temp (T) shifts toward the reactants decrease in temp shifts toward products. N2(g) + 3H2(g) 2NH3(g) + 22 kcal Decrease T Increase T Decrease T Increase T General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Learning Check Predict any shift in equilibrium for each of the following changes on the reaction NH4HS(s) H2S(g) + NH3(g) 1) to products 2) to reactants 3) no change A. H2S(g) is added. B. NH4HS(s) is added. C. NH3(g) is removed. D. A catalyst is added. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Learning Check Indicate if each change on a reaction at equilibrium shifts 2NO2(g) + heat 2NO(g) + O2(g) 1) towards products 2) towards reactants 3) no change A. adding NO(g) B. adding NO2(g) C. raising the temperature D. removing O2(g) E. increasing the volume General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Kinetic Theory and Properties of Gases A gas consists of small particles that move rapidly in straight lines have essentially no attractive (or repulsive) forces are very far apart have very small volumes compared to the volumes of the containers they occupy have kinetic energies that increase with an increase in temperature Gases are described in terms of four properties: pressure (P), volume (V), temperature (T), and moles (n). General, Organic, and Biological Chemistry

Ideal Gas Law The relationship between the four properties (P, V, n, and T) described by the ideal gas law. PV = nRT General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

General, Organic, and Biological Chemistry Learning Check Dinitrogen oxide (N2O), laughing gas, is used by dentists as an anesthetic. If a 20.0 L tank of laughing gas contains 2.86 moles of N2O at 23 °C, what is the pressure (mmHg) in the tank? General, Organic, and Biological Chemistry